1. Field of the Invention
The present invention relates to a heat sink material for releasing heat from a semiconductor component, and to a method for fabricating the same. The present invention also relates to a semiconductor device package or to a heat-release jig equipped with a heat sink formed of the inventive material
2. Background Art
Copper (Cu) is known as a typical material for use as a heat sink. However, although Cu has a relatively high thermal conductivity of 398 W/mK, the coefficient of thermal expansion is also large, having a value of 17 ppm/.degree. C. Thus, when Cu is joined with a semiconductor, such as silicon (Si) having a coefficient of thermal expansion of 4.2 ppm/.degree. C. or gallium arsenide (GaAs) having a coefficient of thermal expansion of from 6 to 7 ppm/.degree. C., both of the joined materials suffer a large thermal stress in the cooling process from the joining temperature to room temperature, or in the cooling process from the maximum temperature achieved during the operation of the semiconductor component to room temperature. In many cases, such a large thermal stress makes the component unfeasible for use. In the light of such circumstances, alloys of Cu with a material having small coefficient of thermal expansion (e.g., W (tungsten) or Mo (molybdenum)), such as CuW and CuMo are used. That is, design of a heat sink material which matches the semiconductor package is made possible by using a material whose coefficient of thermal expansion is controllable. In such cases, however, the alloy becomes inferior to Cu in terms of thermal conductivity, i.e., having a value of about 200 W/mK, because the metals (W or Mo) alloyed with Cu have small thermal conductivity.
Diamond has the highest thermal conductivity in the temperature range of from room temperature to the high temperature region of 200.degree. C. Moreover, the coefficient of thermal expansion thereof in the vicinity of room temperature is about 1.5 ppm/.degree. C., which is smaller as compared with ordinary semiconductor materials such as Si and GaAs.
Therefore, it has been thought of using metallic materials containing particles of diamond embedded therein having such superior characteristics.
The idea of embedding diamond particles is disclosed in, for example, JP-A-Sho62-249462 (the term "JP-A-" as used herein signifies "an unexamined published Japanese patent application"), JP-A-Hei2-170452, JP-A-Hei3-9552, JP-A-Hei4-231436, JP-A-Hei4-259305, JP-A-Hei5-291444, and JP-A-Hei5-347370.
Disclosed in JP-A-Sho62-249462 is a material in which diamond is incorporated in a resin to improve thermal conductivity. However, since a resin generally is a poor conductor of heat, the thermal conductivity as a whole is not much improved.
Disclosed in JP-A-Hei2-170452, JP-A-Hei4-231436, JP-A-Hei4-259305, and JP-A-Hei5-347370 is disclosed a material comprising diamond particles embedded in a metallic matrix. Gold (Au), silver (Ag), copper (Cu), aluminum (Al), magnesium (Mg), etc., are used for the metallic matrix.
Also known (see H. L. Davidson et al., IEEE (1995), pp. 538) is a material based on diamond, which is prepared by subjecting diamond to special coating with a metal, and then impregnating the resulting material with an alloy of Cu and Ag.
All of the cases described above comprises incorporating diamond particles into a metallic matrix. That is, the diamond particles are separated from each other with a metallic material interposed therebetween. Accordingly, heat should also be transferred by the metallic material, that is, by a material sequence ordered in the order of diamond/metal/diamond/metal/ - - - . This structure is disadvantageous not only because thermal conductivity is impaired by the junction formed between diamond and the metallic material, but also because the sample itself cannot be shaped easily due to the weak bonding at the junction between diamond and the metallic material. In fact, the thermal conductivity achieved by a conventional heat sink was found to be 400 W/mK at best.